The present invention relates to a method for producing copper sulfate from waste copper-containing liquid, such as waste liquid formed in the production of PC boards, or formed in washing hardware. More particularly, the present invention relates to a method for producing copper sulfate from waste copper-containing liquid which comprises exactingly controlled conditions and steps so as to reduce the copper content of the waste copper-containing liquid and to increase the yield of the copper sulfate.
Heretofore, the method for treating waste copper-containing liquid (see FIG. 4) includes the step of mixing and neutralizing acidic and basic copper-containing liquid in a tank. After neutralization, the resultant liquid is filtered. The filtrate is directly expelled into the surroundings, and the residue is manually collected into a second tank. An amount of 50% sulfuric acid is added to the second tank for further neutralization of the residue. Thereafter, the resultant liquid is centrifugally dewatered. The liquid portion is directly expelled into the surroundings, and the product residue (copper sulfate) is collected and exposed to sunlight for drying purpose.
The above-mentioned method for treating waste copper-containing liquid is undesirable for causing water pollution due to its high copper content in the post-treated waste copper-containing liquid. Also, the yield and purity of the resultant copper sulfate is rather low.
The following describes and sums up the drawbacks of the conventional method:
a) Direct mixing of acidic and basic copper-containing liquid of high concentration contributes to vigorous reaction and therefore instantaneous rising of temperature, which results in undesirable small particle size of solid copper sulfate. Therefore, when the resultant liquid is filtered and when the filtrate is directly expelled into the surroundings, undersized solid copper sulfate may not be able to be filtered out and removed from the exhausted stream under normal filter condition, resulting in high copper content in the exhausted stream. Also, the loss of solid copper sulfate during filtration represents a lower yield in the product copper sulfate. Moreover, the instantaneous neutralization of acidic and basic copper-containing liquid is readily to produce acidic gases which, if expel to the atmosphere, causes air pollution. PA1 b) As the pH value of the reaction mixture of the acidic and basic copper-containing liquid has not been controlled properly, the concentration of the copper ion (Cu.sup.2+) of the filtrate obtained from the neutralization is always within the range of from 300-10,000 ppm. This concentration is far beyond the upper limit of standard tolerance. PA1 c) After the first neutralization, the residue is manually collected into another tank. When the residue is being taken out from the tank manually, the remaining filtrate may contaminate the solid residue, leaving impurities in the final crystalline product. These impurities have adverse effect on the quality and purity of the final product. PA1 d) As 50% sulfuric acid is continuously added to the second tank for the second neutralization of the residue, the system has to be dewatered continuously in order to prevent the continuous increment in the total volume of the whole system. As has been mentioned previously, the liquid portion which has been removed from the system is directly expelled to the surroundings, continuous addition of the 50% sulfuric acid represent continuous environmental contamination. Moreover, this has caused adverse effect on the yield of the product copper sulfate, i.e., rendering the yield lower than 50%. PA1 e) During the second neutralization and crystallization procedure, sulfuric acid is added directly to the residue with resultant solution stands overnight to form the crystalline copper sulfate. In this manner, the crystal size of copper sulfate is not uniform, and in fact, the range of the crystal size is rather wide. This is one of the most undesirable aspect in crystallization. Also, the crystalline copper sulfate is readily contaminated with copper hydroxide and/or copper oxide under such conditions. Therefore, the conventional method produces only low purity and quality products. Furthermore, owing to the fact that crystallization takes longer time to complete, the tank for carrying out crystallization is inevitably larger for holding the solution for 16-24 hours. Therefore, the production rate of conventional method is considered low. PA1 f) At the completion of the second neutralization, the resultant liquid is centrifugally dewatered and the liquid portion is expelled to the surroundings directly. This causes not only water pollution but also low yield and purity of the resultant copper sulfate. PA1 g) Finally, when the product residue (copper sulfate) has been collected, it is exposed to sunlight for drying purposes in a conventional manner. In this manner, the oversized copper sulfate crystal may not be dried when undersized and average-sized copper sulfate crystal have been dried. Moreover, the product may be contaminated with dirt when exposed to sunlight. The space for carrying out the exposure operation represents another practical problem.